1. Field of the Invention
The present invention is directed generally to optics. More particularly, the present invention relates to optics used in a lithography system.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, light is directed from an illumination system to a patterning device, which may be referred to as a mask, a reticle, an array of individually programmable or controllable elements (maskless), or the like. The patterning device may be used to generate a circuit pattern corresponding to an individual layer of an IC, flat panel display, or other device. This pattern may be transferred onto all or part of the substrate (e.g., a glass plate, a wafer, etc.), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. The imaging may include the processing of light through a projection system, which may include optical components such as mirrors, lenses, beam splitters, and the like. Other components or devices may exist in a lithographic apparatus that may also contain optical components.
Illumination systems in conventional lithographic tools can have relatively high telecentricity error (i.e., beam pointing error) (e.g., on the order of several milliradians). This illumination telecentricity error is magnified at the wafer plane by a 4× (typical) magnification projection optics. Projection optics of maskless systems may have much larger magnifications (e.g., on the order of 267×-400×). For these systems, it would be beneficial for illumination systems to have telecentricity errors 100 times smaller than the magnification of the illumination systems for conventional systems.